Oil and gas reservoirs do not often contain homogeneous geologic properties (e.g. porosity and permeability). For many of such reservoirs, the differences in the permeability (ability to allow fluid flow) among the different geologic layers can vary as much as several orders of magnitude.
In the case of an oil production well, a fluid within the subterranean formation (e.g., aquifer), pressurizes the oil and gas and drives some of the oil in place to a nearby production well where the oil and fluid are co-produced. Permeability (a property that measures the ability to transmit flow) may vary greatly among the geologic layers of rock that contain oil within its porous spaces in the subsurface reservoir. Such a wide variation may cause the fluid drive to be non-uniform, such that the larger amount of fluid may enter the higher permeability geologic layers. As a result, the reservoir may be characterized by the very non-uniform displacement of the oil within the reservoir, with most of the oil being quickly mobilized from high permeability layers. This may leave the oil within the lower permeability layers virtually undisturbed, and result in the fluid exiting production wells having a high water to oil ratio (WOR). In other words, a large amount of water exiting from the production well directly correlates to a decreased amount of oil exiting from the same well, which translates to a well that is not optimized for maximum production and/or is considered not economically feasible.
A production well or producer is a well from which reservoir fluids are extracted to a surface facility. Typically the facility is a series of separators or equipment designed to produce three relatively pure streams of gas, oil, and brine, which are then sent for further processing or directly enter pipelines, storage tanks, disposal/injection wells, or to a flare. Sediment and various undesirable mixtures of solids, oil, and brine normally accumulate at the bottom of a separator and are removed periodically. The well can be cased and cemented with access to the reservoir zones by perforations or an openhole completion where no pipe is used. Alternative completions such as slotted liners or gravel packs are also possible. Typically, the fluids entering the production well will be a mixture of hydrocarbon (gas, oil, condensate or mixtures) and brine. The initial brine is normally the connate brine in the reservoir, but as either injected fluid or aquifer fluid encroaches into the reservoir, the produced brine composition will be a mixture of the various brines present in the reservoir. When either injection fluid or aquifer brine break through at the producer, the produced oil rate declines and the brine rate increases. Some reservoirs will include pattern injection wells as well as have aquifer influx while other wells may either have only pressure support from an aquifer or from injection wells. Both scenarios are included in FIG. 1 for clarity. The subject matter of the present application is strictly limited to injection of a treating fluid into producing wells and not into an injection well as a remedial treatment for reducing the WOR. The treating fluids are typically added into a surface line connecting to the wellhead of the producing well, although some wells have their wellhead on the seafloor and require a different pathway for the injected fluids. Injection can be done into the production tubing, coiled tubing that is in the wellbore and concentric with the tubing, or into a live annulus with a largely unrestricted fluid pathway to the zone of interest.